feat: add MPP Lightning charge client support

[MajorTal]

What changed

• adds ordered, rail-neutral payment preferences to the SDK, CLI, MCP, and OpenClaw surfaces
• adds the exact Run402 MPP Lightning charge profile with fixed-amount BOLT11 validation
• adds Alby Hub NWC as the first supported Lightning wallet adapter
• preserves idempotency, retained-operation, USD, native-amount, routing-fee, and portable-receipt invariants across retries
• updates public reference material and cross-surface parity checks

Why

Run402 now supports MPP Lightning charge negotiation in the gateway. Public clients need to select that method explicitly, pay through a locally held wallet capability, and normalize the outcome into the existing rail-neutral payment result.

Release boundary

This is a draft until production inbound capacity is available and the coordinated gateway/client/docs release is ready. No routine feature flag, shadow path, canary path, or phased activation is introduced.

Closes #537 after the coordinated release is published.

Validation

• npm test — 1,249 passing tests
• deterministic agent-skill artifacts rebuilt and checked
• TypeScript examples across all three public reference documents compiled cleanly